Telephone system



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Jan. 28, 1941.

14 Sheets-Shea? 13 ATTORNEYS Jan. 28, 1941.

T. F. CROCKR TELEPHONE SYSTEM Filed Feb. 17, 1939 14 Sheets-Sheet 14 .BY/gmini, l Y

ATTORNEYS Patented Jan. 28, 1941 UNITED STATES y PATENT OFFICE TELEPHONE SYSTEM Application February 17, 1939, Serial No. 256,901

80 Claims.

The present invention relates to telephone systems and, more particularly, to improved automatic switching apparatus of the character of that disclosed and claimed in the copending application of Thomas F. Crocker, Serial No. 142,558, led May 14, 1937, now Patent No. 2,167,710, granted Aug. 1, 1939, which apparatus is connected and arranged to handle switchboard traic.

A telephone system of this character conventionally comprises an automatic central oflice, a number of distant exchanges of any desired type, and interconnecting toll lines, the central oiice and each of the distant exchanges serving local subscriber substations provided with subscriber lines. Local calls in the central ofce and in the distant exchanges of the automatic type are completed under the control of the subscribers at the subscriber substations; local calls in other of the distant `exchanges are completed in any suitable manner; and calls between the central ofilce and the distant exchanges are completed by operators at a switchboard provided in the Central office. More particularly, the switchboard which is provided in the central office comprises a number of operator positions, including groups of inward or toll operator positions, combined line and recording or C. L. R. operator positions, and delayed or point-to-point operator positions.

In handling traffic at the switchboard, incoming calls from the distant exchanges are first routed by way of the toll lines to the toll operator positions at the switchboard and then completed therefrom directly to the local subscriber substations in the central oiilce, or transferred therefrom to the point-to-point operator positions to be completed later. Also, through calls between the distant exchanges and including the central oiiice are iirst routed by way of the toll lines to the toll operator positions at the switchboard and then extended therefrom by way of the toll lines to others of the distant exchanges. Outgoing calls originating at the subscriber substations in the central oflice which are to be extended to distant exchanges are first routed by 4 ther-eat rst completes a connection to the called toll line orsubscriber substation and then completes a connection to the calling toll line or subscriber substation. p

The various toll and trunk calls are routed to and extended from the diierent operator positions by automatic switching apparatus including both local and toll switch trains, whichapparatus is distributed for use and governed by sultable control means. Also, apparatus is provided at each operator position for answering calls routed thereto, for supervising calls completed by way of the operator position, and for controlling the switching apparatus, thereby to extend and to initiate calls from the operator position. Furthermore, apparatus at each operator position is provided for performing the various functions over the different toll, trunk and vsubscriber lines.

It is an object of the presen-t invention to provide, in a telephone system of the character described and including a toll switch train associated with an. operator position and a local switch train having access to 'a telephone line extending to a. Itelephone station, an improved trunk circuit disposed between the toll switch train and the local switch train which is so connected and arranged that a connection between the operator position and the telephone station may be controlled and supervised in an improved manner.

It is another object of the invention to provide, in a telephone system of the character described, a toll switch train associated with the operator position including an automatic switch which is connected and arranged in an improved manner.

Another object of the invention is to provide, in a telephone system of the character described 'and including a number of operator positions and a group of trunk lines, an improved distributor arrangement for assigning the trunk lines to be taken for use and for routing calls on the trunk lines taken for use to the operator posiscribed and including a number of operator positions and a distributor for routing incoming toll and trunk calls to the operator positions to be answered, operator controlled means at each of the operator positions for selectively converting the associated operator position froma universal toll and C. L. R. operator position to'a toll operator position and to a point-to-point voperator position. f

It is a further object of the invention to provide, in a ytelephone system of the character described and comprising a central oflice provided with a number of operator positions and a community automatic exchange or C. A. X. network including a number o! exchanges and a number oi' trunks extending therebetween, an improved arrangement for completing calls between the exchanges in the C. A.*X. network by way of the trunks and from the operator positions. l

The invention is illustrated as being embodied in a telephone system comprising a central oillce of the automatic type. a community automatic exchange or C. A. X. network including a number of exchanges of the automatic type, and a distant exchange of any suitable type.` 'I'he central oiilce serves a number of local subscriber substations and a number oi local paystations; while the distant exchange'and each of the exchanges in the C. A. X. network serve a number of local subscriber substations. Local switch trains are provided in the central omce and in each of the exchanges in the C. A. X. network, thereby to permit the local subscribers in the respective exchanges to complete local calls; while local calls in the distant'exchange are completed in any desired manner.

The C. A. X. network includes a tandem exchange and a number of other exchanges. Trunk lines are arranged. between the other exchanges and the tandem exchange in the C. A. X. network; C. A. X. trunks are arranged between the tandem exchange in the C. A. X. network and the central office; while toll lines are arranged between the distant exchange and the central oilice. Also, C. L. R. trunks are arranged in the central omce which are accessible to the local switch train therein.

A switchboard is arranged in the central oillce which com-prises a number of operator positions; Furthermore, a toll switch train is arranged in the central oice which comprises a number of groups of iinder-selector links individually associated with the operator positions at the switchboard and a group of delayed toll selector switches. Each of the finder-selector links includes a finder switch and a toll selector switch. Each of the nder switches of the finder-selectorlinks has access to each oi the delayed toll selector switches, to each of the C. L. R.. trunks, to each of the paystation lines in the central oice, and to each of the C. A. X. trunks; while each of the toll selector switches has access to the local switch train, to each of the paystaton lines, to each of the toll lines, and to each of the C. A. X. trunks. The local switch train comprises a number of finder-selector links each including a ilnder switch and a selector switch, and a number of connector switches accessible to the selector switches. Furthermore, a combined local and toll connector switch is provided in the central oiiice which is accessible to the selector switches of the local switch train and to .the toll and delayed toll selector switches of the toll switch train. The local connector switches have access to the local subscriber lines; while the combined local v anemona and tollV connector switches have access to the lzal subscriber lines and to the local paystation es, A

Also, apparatus is arranged at each of the operator positions for governing the operation of the nder-selector ylinks associated therewith, thereby to answer, to extend, to initiate, and to supervise calls by way oi the associated flnderswitches of the local switch train, which trunk circuit comprises a trunk line including first and second branches. 'I'he first branch of the trunk line is accessible to the toll and delayed toll selector switches of the toll switch train; and the second branch oi' the trunk line is individually associated with a corresponding one of the local connector switches of the local switch trains. Means under the control of the operators at the operator positions are provided for causing the toll and delayed toll selector switches of the toll switch train to seize the ilrst branches of the trunk lines and then to cause the local connector switches of the local switch train associated with the second branches oi' the trunk lines to seize the subscriber lines, thereby to extend calls from the operator positions to the subscriber substations associated with the subscriber lines. A signal is provided at each of the operator positions, each of which is actuated under the control of any one of the trunk circuits when the call is extended to the subscriber substation and arrested under the control of the trunk circuit when the call is answered at the subscriber substation. Furthermore, each of the trunk circuits comprises a normally completed metallic connection between the 'rst and second branches of the trunk line and a repeater, the trunk circuit being so connected and arranged that the metallic connection between the first and second branches of the trunk line is interrupted and an operative connection is completed therebetween by way of the repeater when a call is extended thereover to a subscriber substation. Finally, each of the trunk circuits is so connected and arranged that the signal at any one of the operator positions may be actuated under the control of the subscriber at one of the subscriber substations, thereby to give the subscriber at the subscriber substation switchhook supervision in order to signal the operator at the operator position.

Also, a trunk circuit of the general character of that described above is arranged between the toll selector switches of the toll switch train and each of the combined local and toll connector switches, each of the last-mentioned trunk circuits being further connected and arranged to control the operation of the associated combined local and toll connector switch to cause ringing current t'o be projected over `a seized paystation line. Furthermore, each of the last-mentioned trunk circuits is further connected and arranged to control by way of the associated combined local and toll connector switch the collection and refund of coin at a paystation associated with a paystation line seized by the associated combined local and toll connector switch.

In accordance Awith another feature of the invention, each of the toll and delayed toll selector switches in the vtoll switch trainv is of the type comprising a wiper set movable in both longitudinal and lateral directions, an associated contact bank provided with a number of longitudinally spaced-apart rowsy of laterally spacedapart contact sets, driving means for moving the wiper set with respect to the contact bank in a longitudinal direction and in a lateral direction, and a control network for governing the driving means. In each of the switches a first group of lines is terminated by contact sets disposed in a first row in the contact bank thereof; and a second group of lines is terminatedby contact sets disposed in a second and a third row in the contact bank thereof. Furthermore, operator controlled means is provided at each of the operator positions for controlling the control network in each of the switches, and each of the control networks is so connected and arranged that the associated driving means is selectively governable to cause the associated wiper set selectively to engage a contact set in the associated contact bank terminating an idle line in the rst group, a contact set in the associated contact bank terminating an idle line in the second group, and a contact set in theassociated contact bank terminating any particular line in the second group. More particularly, each of the control networks is impulse responsive and responds to a given single digit to cause the associated switch to seize an idle line in the first group, to two given successive digits to cause the associated switch to seize anidle line in the second group, and to two other successive digits to cause the associated switch to seize a corresponding particular line in the second group.

In accordance with another feature of the invention, a CQL. R. trunk distributor is'provided in the central oice for causing the selector switches in the local switch train to seize in a predetermined order idle ones of the C. L. R. trunks. Further, a position distributor is provided for selecting in a predetermined order the groups of iinder-selector links individually associated with the operator positions of the switchboard in which there are previously prepared links, operator controlled means being provided at each of the operator positions for preparing any one of the finder-selector links in the associated group of links to be'selected by the position distributor. Furthermore, the C. L. R. trunk distributor is so connected and arranged that when a selector switch in the local switch train operates to seize an assigned C. L. R. trunk, it operates to cause another idle C. L. R. trunk to be assigned to be seized. Also, the C. L. R. trunk distributor operates to cause the position distributor to operate, thereby to cause a prepared one of the finder-selector links in a selected one of the groups to operate, whereupon the last-mentioned nder-selector link seizes the C. L. R. trunk which has been seized by the selector switch of the local switch train.

Means is provided in the tandem exchange for causing the C. A. X. trunks to be seized in a predetermined order, and a C. A. X trunk distributor is provided in the central oiiice, which is operative to cause the position distributor to operate, vthereby to cause a prepared one of the nderselector links in a selected one of the groups to operate and seize the C. A. X. trunk which has been seized in the tandem exchange. Furthermore, the C. A. X. trunk distributor is so connected and arranged that it causes the C. A. X. trunks to be seized in a predetermined order by the under-selector links.

Furthermore, the C. L. R. trunk distributor is normally operative in response to the presence of a call on any one of the C. L. R trunks and remains operated `until all of the calls on the C. L. R. trunks are answered at the switchboard; while .the C. A. X trunk distributor is normally operative in response to the presence of a call on any one of the C. A. X. trunks and remains operated until all of the calls on the C. A.v X. trunks are answered at the switchboard.

In accordance with a further feature of the invention, the C.v L. R. trunk distributor and the C. A. X. trunk distributor are so interrelated that when one of these distributors is'operated, the other of these distributors is prevented from lbeing operated, thereby to cause all of the calls of one type to be answered before any of the calls of the other type are answered, the type of calls first answered depending upon the type of call first extended to the switchboard. Moreover, the C. A. X. trunk distributor is so connected and arranged that it is relatively slow to operate; whereas the C. L. R. trunk distributor is so connected and arranged that it is relatively fast to operate. Accordingly, in the event a C. A. X. trunk call and a C. L. R. trunk call are simultaneously initiated, the C. L. R. trunk call is rst answered at the switchboard.

In accordance with a further feature of the invention, the position distributor is normally operative to cause a prepared one of the finderselector links in a selected one of the groups to operate and route both toll and trunk calls to the associated operator position to be answered. Operator controlled means is provided at each of the operator positions for restricting the operation of the position distributor, whereby only toll calls are routed to the associated operator position to be answered. Additional operator controlled means is provided at each of the operator positions for preventing the position distributor from selecting any one of the finder-selector links in the associated group when a delayed call is initiated at the associated operator position.

In accordance with another feature of the invention, switching means is provided in the tandem exchange which is controlled over calling ones of the lines in the C. A. X. network and which has access to the C. A. X. trunks. Also, rst and second switching devices are associated with each of the C. A. X. trunks in the tandem exchange and have access to each of the lines in the C. A. X. network. Apparatus is provided in the tandem exchange which is so connected and arranged that when the switching means seizes one of the C. A. X. trunks, the associated first switching device is rendered operative by way of the C. A. X. trunk from any one of the operator positions at the switchboard in the central oice. At this time, after the call on the C. A. X. trunk is answered at one of the operator positions at the switchboard in the central oice,

the associated first switching device is controllable from the operator positionin order to seize any one of the lines in the C. A. X. network, thereby to complete in the C. A. X. network an operative rever-ting call connection between the calling and called lines. Further, it is noted that the operator at the operator position at the switchboard retains supervision of the completed connection and may release` the rst switching device without releasing the connection between the calling line and the C. A. X. trunk. Accordingly, the operators at the operator positions at the switchboard may establish and supervise reverting call connections in the C. A. X. network.

Further, the apparatus in the tandem exchange is so connected and arranged that when one of the C. A. X. trunks is seized from one of the operator positions at the switchboard in the cen- 5 tral oflice upon an outgoing call from the central ofllce to the C. A. X. network, the associated second switching device is rendered operative by way of7 the C. A. X. trunk in order to establish a connection to any one of the lines in the C. A. X. network. Accordingly, the operators at the operator positions at the switchboard in the central office may extend outgoing calls to any one of the lines in the C. A. X. network. Further, -it is noted that the apparatus in the tandem exchange is impulse responsive and operator controlled means is provided at each of the operator positions at the switchboard for controlling by way of a seized one of the C. A. X, trunks the first or second switching device operatively associated therewith, the switching device operatively associated with a seized C. A. X. trunk depending upon whether the C. A. X. trunk is seized upon a call from the C. A. X. network to the central office or upon a call from the central oiiice to the C. A. X. network. Moreover, it is noted that the impulse responsive apparatus in the tandam exchange is controlled over any one of the C. A. X. trunks by way of a simplex link including the C. A. X. trunk. Also, a trunk circuit is associated with each of the C. A. X. trunks, which trunk circuit is so connected and arranged that both the calling and ,called lines in the C. A- X. network are given switchhook supervision in order to signal the operators at the operator positions at the switchboard.

Further features of the invention pertain to the particular arrangement of the circuit elements of the system, whereby the above-outlined and additional operating features are attained.

'I'he novel features believed to be characteristic of the invention are set forth in the appended claims. 'I'he invention, both as to its organization and method of operation, together with further objects and advantages thereof, will best be 45 understood by reference to the following specication taken in connection with the accompanying drawings, in which Figure 1 illustrates the general arrangement of a telephone system embodying the present invention; Figs. 2 to 15, inclusive, taken together, illustrate the details of a system having incorporated therein the features of the invention as briefiy outlined above; and Fig. 16 illustrates the mode of combining Figs. 2 to 15, inclusive, to form a unified system.

DEsoRiP'rIoN 0F rm: APPARATUS INCORPORATED 1N THE TELEPHONE SYSTEM Referring now more particularly to Fig. 1 of the drawings, the telephone system there illustrated comprises a central ofiice A, a distant exchange B, a distant community automatic exchange or C. A. X. network including a tandem exchange C and two exchanges D and E associated therewith. The central office A and each of the exchanges B, C, D and E serve a number of local stations, the local stations served by the central oiilce A including both subscriber substations and paystations. More particularly, the central ofiice A serves a number of local subscriber substations, including the subscriber substation indicated at TI and associated with the subscriber line 962 extending to the central office, and a number of paystations, including the paystation indicated at T2 and associated with the paystation line |50| extending to the central omce; while the tandem exchange C serves a number of subscriber substations, including the subscriber substation indicated at T3 and associated with the subscriber line 033 extending to the tandem exchange. The central ofilee A and the distant exchange B are interconnected by a group of two-way toll lines of the ring-down type, including the toll line indicated at 340. The central ofllce A and the tandem exchange C are interconnected by a group of two-way trunks, including the trunk indicated at 5|0. The tandem exchange C is interconnected with the exchanges D and E by two groups of trunks respectively including the trunks indicated at 532 and 53|. Each of the toll lines extending between the central oiiice A and the distant exchange B terminates in a ring-down toll line circuit individual thereto, the ring-down toll line circuit 3|0 being individual to the toll line 340. Each of the trunks extending between the central ofllce A Aand the tandem exchange C terminates in a trunk circuit individual thereto, the trunk circuit 600 being individual to the trunk 5|0. Each of the subscriber and paystation lines extending to the various exchanges is provided with a line circuit individual thereto, the subscriber line 962 extending to the central oiiice A being provided with a line circuit 96| individual thereto, and the paystation line |50| extending to the central ofiice being provided with a line circuit |500 individual thereto. 'Ihe central oice A and each of the exchanges C, D and E are of the automatic type, while the distant exchange B may beof any desired type. Accordingly, the central oflice A and each of the exchanges C, D and E are provided with local switch trains which preferably comprise a plurality of groups of finder, selector and connector switches of the Strowger type arranged in the usual manner in order to set up the various connections between the local subscriber substations in the central oflice A and in the exchanges C, D and E. More particularly, the central office A is provided with a local switch train including the finder switch 41|, the selector switch 412 and the connector switch 410. A number of reverting call switches, including the reverting call switch 413, are provided in the central ofllce A and are accessible to the selector switches in the local switch train therein, thereby to permit local reverting calls to be completed from the local subscriber substations in the central office A. Also, the central office A is provided with a. toll switch train, which preferably comprises a pluralityI of groups onf finder, selector and connector switches of the Strowger type arranged in a manner more fully described subsequently, and which is utilized in setting up the various toll 'and trunk connections in a manner hereinafter described.

An automatic dial switchboard is arranged in the central oflice A and comprises a groupv of operator positions, each operator position having access to the toll switch train for the purpose of setting up the various toll and trunk yconnections.

More particularly, the toll switch train comprises a plurality of groups of finder-selector links individually associated `with the operator positions at the toll board. The link finder switch 100 and the toll selector switch 000 comprise one of these links which is included in a group of links individually associated with the first operator position indicated at |400. Also; avgroup of combined line and recording or C. L. R. trunks, including the C. L. R. trunk 450, is provided in the central ofiice A, which trunks are accessible to the selector switches of the local switch train. More particularly, the C. L. R. trunk 450 is accessible to the selector/switch 412 of the local switch train. Also, a C. L. R. trunk circuit is individually associated with each of the C. L. R. trunks, the C. L. R. trunk circuit 400 being individually associated with the C. L. R. trunk 450.

Each .of the nder switches of the nderselector links has access to each of the C. L. R. and C. A. X. trunks, to each of the toll lines extending between the central ofllce A and the distant exchange B, to each of a group of delayed toll selectors, including the delay toll selector 480, included in the toll switch train, to each oi the paystation lines in the central oiiice A, and to the trunk circuit at the associated operator position. More specicaily, the finder switch 100 of the finder-selector link illustrated has access to the C. L. R. trunk 450 by way of the trunk line 460,

to the C. A. X. trunk |0 by way of the trunk line 610, to the toll line 340 by way of the trunk line 32|, to the delayed toll selector switch 400 by way of the trunk line 415, and to the paystation line |50| by way of the trunk line |5|4. Furthermore the finder switch 100 is accessible to the trunk circuit at the rst operator position 400 by way of the cable |286. Also, each of the toll and delayed toll selectors has access to each of the .toll lines extending between the central oce A and the distant exchange B, to each of the C. A. X. trunks, to a group of local connector switches included in the local switch train, and to a group of combination local and toll connector switches. More specically, the delayed toll selector 480 and the toll selector 800 each has access to the toll line 340 by way of the trunk line 320, to the C. A. X..trunk 5|0 by way of the trunk line 680, to the local connector switch 960 by way of the trunk line 050, and to the combination local and toll connector switch |090 by way of the trunk line |080.

Also, it is noted that on outgoing trunk circuit is interposed between each individual local connector switch and each individual combination local and toll connector -switch and,the delayed toll and toll selectors. More particularly, the outgoing trunk circuit 900 is individually interposed between the local connector switch 960 and the trunk liney 950 extending to the delayed toll selector switch 480 and to the toll selector switch 000; and the outgoing trunk circuit |000 is individually interposed between the combination local and toll connector switch |090 and the trunk line |080 extending to the delayed toll selector 680 and to the toll selector switch 800.

.The local connector switches have access to each subscriber line terminating at the central oiiice A; and the combination local and toll connector switches have access to each paystation line terminating at the central oilce A, thereby to permit toll and trunk connections to be extended to the local subscriber substations and paystations in the central oiiice.

Preferably, each of the operator positions, including the rst operator position |400 at the switchboard in the central oiTice A, is of the universal type, thereby rendering it possible to render toll, C. L. R. and point-to-point service at each operator position. Also, each operator position is so connected and arranged that the service rendered thereby may be restricted to toll service. Common start and position distributor apparatus 330 is associated with the operator 4positions at the switchboard, this apparatus being so connected and arranged that incoming calls to the switchboard' are routed in a predetermined order to the operator positions to be answered.

Also, C. L. R. and C. A. X. trunk distributors '20| and 202, respectively, are provided which arev so connected and arranged that C. L. R. and C. A. X. trunk calls arc routed to the various operator positions to be answered in a predetermined order. More particularly, these distributors are so connected and arranged that all trunk calls of a particular type are routed to the various operator positions to be answered before any of the trunk calls of the other type are routed to the various operator positions to be answered, the type of calls answered iirst being determined by the type of the first incoming call to arrive at the switchboard. This arrangement insures that all of the calls of a given type are answered before any of the calls of the other type are answered.

Also individually associated with each operator position are one or more sender control circuits, the sender control circuit 300 being individually associated with the tlrst operator position |400. Also, at each operator position there is provided a sending keylset individual thereto which is associated with each of the sender control circuits associated with the operator position, the sending key set 303 being individually associated with the iirst operator position |400 and with the sender control circuit 300. Finally, a group of digit register and control circuits is commonly associated with the switchboard. Each of the sender control circuits is provided with switching apparatus having access to each of the digit register and control circuits and is operative to select an idle digit register and control circuit when the sender control circuit is taken for use. Also, each of the sender control circuits is provided with switching apparatus having access to the trunk circuit at the operator position individual thereto and to each of the finder-selector links individually associated with the particular operator position. More specifically, the-sender control circuit 300 is individually associated with the first operator position |400 by way of the trunk dine 343 and is operatively associated with the sending key set 303 by way of the trunk line 342. Also, the sender control circuit 300 has access to the digit register and control circuit 304 by way of the trunk line 34|, to the trunk circuit at the first operator position |400 by way of the cable |361, and to the toll selector switch 800 of the finder-selector link illustrated by way of the cable 136.

Preferably, the elements of the C. A. X. network, as best shown in Fig. 5, are connected and arranged in the manner described and claimed in U. S. Patent No. 1,759,869, Norman H. Saunders, granted May 27, 1930. Briefly, the C. A. X. network comprises a tanden exchange C and two exchanges D and E interconnected by two groups of trunks respectively including the trunks 532 and 53|. Individually associated with each of the trunks extending between the tandem exchange C and the exchanges D and E is a line switch, the line switch 52| being individually associated with the trunk 532 and the line switch 522 being individually associated with the trunk 53|.

Also arranged in each of the exchanges C, D ando E is a local switch train which is utilized in completing local calls in the particular exchange. More specifically, the local switch train included in the tandem exchange C comprises a group of line switches individually associated with the subscriber lines terminating thereat, the line switch 520 being individually associated with the subscriber line 633, a plurality of selector switches, including the selector switch 5 I 8, accessible to each of the line switches, and a plurality oi connector switches, including the connector switch 6|9, accessible to each of the selector switches and having access to the subscriber lines. Preferably, each of the line switches is of the well-known rotary type, while each of the selector and connector switches is of the wellknown Strowger type.

Also included in the tandem exchange C is a group of trunk lines, each trunk line including a number of branches, the trunk line illustrated including the branches 502, 503 and 504. Each of the trunk lines included in the tandem exchange C is accessible to each of the line switches in the groups of line switches respectively including the line switches 52| and 522 and to each of the selector switches in the group including the selector switch 5|8. Also, a control circuit and repeater is individually associated with each trunk line in the tandem exchange, the control circuit and repeater 500 being individually associated with the trunk line illustrated.

Preferably each of the trunk lines is connected and arranged in the manner of the trunk line indicated, the branches 50| and 502 being individually provided with the selector switches 5|6 and 5H, respectively, and the branch 504 being associated with the C. A. X. trunk line 5|0 extending to the central oiiice A. More particularly, the control circuit and repeater 500 associated with the trunk lineillustrated is so connected and arranged that ordinary trunk calls may be extended from the central oice A over the C. A. X. trunk line 5|0 and the control circuit and repeater 500 by way of the selector switch 5|6 to the local switch train in the tandem exchange C or to the local switch trains in either of the exchanges D or E. Also, the control circuit and repeater 500 is so connected and arranged that a dual or reverting call may be set up -from the central oiiice A over the C. A. X.

trunk line 5|0 by way of the control circuit and repeater 500 and the selector switch 5|'l to the local switch train in the tandem exchange C or to the local switch train in either the exchanges D or E, while the branch 503 of the trunk line illustrated is seized by one of the selector or line switches having access thereto. Also, it is noted that the control circuit and repeater 500 individually associated with the C. A. X. trunk line 5|0 is controlled over the branch 503 of the trunk illustrated and over the control conductor C5|5, the last mentioned control conductor being connected to the neutral point between two impedance elements 5|3 and 5|4 extending between the line conductors C5|| and C5|2 of the C. A. X. trunk line 5| 0, thereby to provide a simplex link. Finally, it is noted that the line conductors C505 and C506 of the -branch 504 of the trunk line illustrated are capacitively coupled to the line conductors C5|| and C5|2, respectively, of the C. A. X. trunk line 5|0Vby the condensers 501 and 508, respectively.

Preferably, each of the trunk circuits terminating the C. A. X. trunks in the central oflce A is identical to the trunk circuit 600 terminating the C. A. X. trunk 5|0. As best shown in Fig. 6, the trunk circuit 600 comprises a repeater 633 operatively associated with the C. A. X. trunk 5|0 and with the trunk lines 610 and. 680' extending to the finder-connector links disposed at the switchboard. Also, the trunk circuit 600- comprises a relay network including a start relay R640, a dial-out relay R620, a marking relay R650 and a number of control relays R6|0,V

R630 and R660 connected in a manner more fully described subsequently.

Preferably, each of the C. L. R. trunk circuits terminating the C. L. R. trunks in the central and R440 connected and arranged in amanner more fully described subsequently.

Preferably, each of the trunk circuits included in each of the trunk lines extending to each of the local connector switches is identical tothe trunk circuit 900 which comprises, as best shown in Fig. 9, a repeater 9|0 operatively associated with the trunk line 955 extending to the local connector switch 960 and with the trunk line 950 extending tothe toll selector and delayed toll selector switches. comprises a relay network including a number of control relays R920, R930 and R940 connected and arranged in a manner more fully described subsequently. Preferably, each of the trunk circuits included in each of the trunk' lines extending to the combined local and toll connector switches is identical to the trunk circuit |000 which comprises, as best shown in Fig. 10, a repeater |0|0 operatively associated with the trunk line |084 extending to the combined local and toll connector switch |090 and with the trunk line |080 extending to the toll selector and delayed toll selector switches. Also, the trunk circuit |000 comprises a relay network including a number of control relays R|020, R|030, R|040, R|050, R|060 and R|0'l0 connected and arranged in a manner more fully described subsequently.

Preferably, each of the line circuits termimating the toll lines in the central oiilce A is identical to the line circuit 3|0 which is, as indicated in Fig. 3, a ring-down toll linecircuit of any suitable connection and arrangement. The specific connection and arrangement of the ,ring-down toll line circuit 3|0 is not disclosed as the details thereof form no part of the present arrangement.

Preferably each of the line circuits terminating the subscriber lines extending to the central oiiice A from local subscriber substations is identical to the line circuit 96| which is, as indicated in Fig. 9, a substation line circuit of any suitable connection and arrangement. The specic connection and arrangement of the substation line circuit is not disclosed as the details thereof form no part of the present invention.

Preferably, each of the line circuits terminating the paystation lines extending to the central oiiice A from local paystations is identical to the paystation line circuit |500 which comprises, as bestl shown in Fig. 15, a number of control relays R|520, R|530 and AR|540 rconnected and arranged in a manner more fullv described subsequently.

The C. L. R.`trunk distributor 20| and the C. A. X. trunk distributor 202 are so connected and, arranged that C. L. R. trunk calls and Also, the trunk circuit 900` 

